During production of electronic circuit boards and especially of double sided circuit boards a pattern of solder paste is printed on the circuit board prior to placing and soldering of electronic components to the circuit board using reflow solder methods. For proper application of solder paste the circuit board has to be held in a desired position with high precision, and it has to be supported in various locations to prevent any bending of the circuit board during the printing process.
The prior art includes vacuum tables with sidewalls which can be adjusted to the size of the particular printed circuit board to be handled. None of the known vacuum tables includes a plurality of openings, arranged in rows and columns, which can be closed off, inside and outside of the vacuum chamber, and which can be used for positioning support posts for the printed circuit board or left open inside the vacuum chamber to apply a vacuum. None of the prior art systems has a number of different types of support posts, such as support posts with centric or off-center supports, and support posts with suction cups to improve holding power on the printed circuit board during the printing operation.
The universal suction plate of the present invention prevents damage of electronic components during an application of e.g. a pattern of solder paste, on the second side of a printed circuit board. While printing on the second side of a printed circuit board the first, lower side contains components, such as capacitors, resistors, integrated circuit of different sizes and heights, which can not be used for supporting the printed circuit board. The universal suction plate is used in combination with a printing apparatus, and a conveyor system for supplying printed circuit boards and removing the same after the print operation. The suction plate for holding and supporting electronic circuit boards is placed underneath and aligned with the printing apparatus. The conveyor system supplies the circuit boards to the suction board, which includes sensors to determine the position of a circuit board. A separate apparatus lifts the suction plate to the lower plane of the circuit board. A strong vacuum is generated in the suction chamber or one or more suction cups to hold the circuit board in place. To avoid any buckling or bending of the circuit board by the vacuum and during the print operation, support posts of different forms and shapes are provided at various locations underneath the circuit. After completion of the print operation the vacuum is released, the suction plate is lowered, and the circuit board is forwarded by the conveyor system to the next production step.
The suction plate includes a base plate and a support plate with a large number of openings for receiving support posts and sensors. The base plate includes a connector to a vacuum pump. A space between base plate and support plate connects the vacuum pump with the selected openings in the support plate and at least a vacuum chambwe or a vacuum suction cup.
The vacuum chamber is defined by walls which are movable in accordance with the size of the circuit board to be handled in the printing operation. Attached to the sidewalls of the vacuum chamber or the support platw there are sensors which detect when a conveyor system supplies a new circuit board. The sensors control the conveyor system to advance the circuit board to the proper print position. A Z-axis drive lifts the suction plate until the circuit board rests in the side walls of the vacuum chamber or the support posts on the support plate. The vacuum is applied and the print operation can be performed. Additional positioning means can be used to move a circuit board to a desired position with high accuracy independent of the conveyor system.
The vacuum generated underneath the circuit board is of sufficient strength to overcome leakage of air into the chamber through openings in the circuit boards, such as vias, and minor openings in the movable side walls.
The support means are placed in suitable ones of a large number of openings in the support plate. These support means include plain support posts, posts with offset extensions, posts with suction cups. These different types of posts are required to maintain circuit boards in a plane position. The supports are positioned directly under the circuit board and do not interfere with any of the components on the lower side of the circuit board, where these components reach into the vacuum chamber. The posts with offset extensions are used to support the circuit board at locations which do not align with an opening in the support plate.
Support posts with suction cups are used to further inhibit bulging against the vacuum of the circuit board, and to further reduce horizontal movement of the printed circuit board during the print process. These suction cups are connected through the support posts to the vacuum generator.
Short cavity plugs are provided to seal unused openings in the suction plate, and especially all of the openings outside a vacuum chamber.